Catalyst systems, which are solutions of one or more catalyst components (e.g. a transition metal compound and optionally a cocatalyst) are known in the field as homogeneous catalyst systems. Homogeneous systems are used as liquids in the polymerisation process. Such systems have in general a satisfactory catalytic activity, but their problem has been that the polymer thus produced has a poor morphology (e.g. the end polymer is in a form of a fluff having a low bulk density). As a consequence, operation of slurry and gas phase reactors using a homogeneous catalyst system cause problems in practice as i.a. fouling of the reactor can occur.
In the patent publications WO03/000757, WO03/000754 and European Patent Application No. 01660238.5 from the same applicant, the above mentioned problem has been overcome by introducing a new process for producing Ziegler-Natta (ZN) or Single-Site-catalyst (SSC) components, in which the catalyst is formed in a dispersed phase containing the preponderance of the reactive compounds of a produced oil-in-oil emulsion and subsequently this dispersed phase being solidified, e.g. by heating, to provide the respective catalyst component.
The particle size of the catalyst particles described in the above applications can be controlled by the size of the droplets of the dispersed phase, and spherical particles with an uniform particle size distribution can be obtained.
Therefore, these catalyst components have excellent morphology and good particle size distribution and the polymer particles produced by using this catalysts have very good morphology properties, too.
However, the methods for preparing the catalysts described in the above applications usually require a washing step followed by drying the washed catalyst components. After settling and siphoning the washed solids were dried, for instance by evaporation or flushing with nitrogen at elevated temperatures. This drying step can reveal significant disadvantage, as the catalyst yield might be decreased while the catalyst tends to stick in the catalyst dryer and thus a significant part of the catalyst might be lost. Furthermore, catalyst yield might also be decreased as portions of the catalyst could be left inside the reactor after preparation. Not to mention, that the drying step in such a procedure is a very critical step, during which the catalyst morphology will be deteriorated, i.e. the good catalyst particle morphology obtained in the preparation procedure will always be destroyed to some extent during the drying step, which in turn has undesired effects on the polymerisation procedure. In addition catalyst activity might be decreased a lot, and furthermore, the drying step needs of course time and causes additional costs. Still one disadvantage relates to the activity losses of the dried catalysts during the catalyst storage.
Therefore, an improved method for preparing catalyst component is required in order to increase yield, to keep or even improve the catalyst morphology, to at least maintain or even increase the catalytic activity during the whole preparation procedure. Further the improved method is needed to decrease preparative effort and time on one side and, on the other side to reduce the production costs for the catalyst, and finally to reduce catalyst activity losses during the storage and difficulties during transportation.
The inventors have surprisingly found that, when preparing an olefin polymerisation catalyst component by using a fluidic isolation medium, such as oil-like fluid, the drying step for the catalyst particles after the washing procedure can be avoided, whereby a homogenous olefin polymerisation catalyst component in a form of a fluidic slurry can be obtained, which is as such ready for use.
The use of oils or waxes e.g. as a catalyst carrier in a catalyst preparation process is known in the prior art. However, said oils or waxes are to be very viscous and are used for making feeding of the catalyst into the polymerisation process much more easier. The catalyst itself is produced according to an usual manner, i.e. the processes comprise always the drying step, which can now, according to the present invention, be avoided.
Other uses of oils are described, for instance in U.S. Pat. No. 5,641,721, which discloses a method, in which a viscous oil or a wax is used in a process wherein a supported procatalyst composition is pre-polymerised with a monomer in a viscous substance to produce a supported pre-polymerised wax catalyst composition. According to an important object of said application, the viscosity of the used medium (oil or wax) has to be so high that the negative effect of settling can be avoided. Further, in EP 0083074, an oil is used to form dispersions or emulsions of liquid catalyst compositions.
However, none of said references deal with the use of a fluidic medium for isolation of Ziegler-Natta or Single-Site-catalysts prepared by an emulsion method without using any external carrier in subsequent treatment for prepared catalyst particles after the washing step and for improving the catalyst properties and its preparation process. None of the references above disclose a method where use of fluidic isolation medium is part of the catalyst preparation method, in which method there is no need to isolate the catalyst as dry catalyst powder or catalyst product. This means that the critical drying step, which has many negative effects on catalyst properties, can be avoided. Furthermore, in contrast to the prior art, settling of the prepared catalyst particles causes no harm in the present invention, it could be even desired.
Details of the present invention will be discussed more precisely below.